1. KEY CONCEPT Infections can be caused in several ways.

2. Viruses, bacteria, viroids, and prions can all cause infection.
Any disease-causing agent is called a pathogen.
1 nanometer (nm) = one billionth of a meter
100 nm
eukaryotics cells 10, ,000 nm
viroids nm
viruses nm
prokaryotics cells ,000 nm
prion 2-10 nm

3. A virus is made of DNA or RNA and a protein coat.
non-living pathogen
can infect many organisms
A viroid is made only of single-stranded RNA.
causes disease in plants
passed through seeds or pollen

4. A prion is made only of proteins.
causes misfolding of other proteins
results in diseases of the brain